Providing absorbent articles with additives is common. In quite a number of cases, such additives are intended to be transferred to the skin. The additive may be, for example, an oil for lubricating and protecting the skin from drying out or an odor inhibitor which is intended to reduce unpleasant odors from menstrual fluid, urine, fecal matter and the like. It is also known to add agents such as anti-inflammatory products in order to prevent infections or strengthen the defenses of the body against them
There are a number of different solutions for adding an additive to an absorbent product. One of the methods is quite simply to apply additives to the surface layer or the absorbent body. The additive can be, for example, squirted, sprayed, printed or spread onto the absorbent article in order to be released during use. In those cases where the additive cannot be added directly in the form it has in its natural state, it can be applied in the form of a solution, a dispersion or an emulsion.
In those cases where the additive is intended to be transferred to the skin, it is a disadvantage of applying the additive directly to the product that there is a risk of a large part of the additive remaining in the absorbent article and never reaching the skin. The benefit from the additive is therefore low, and the product is costly if the additive is expensive. It is also the case that if the additive is sensitive to moisture or air and is broken down or otherwise destroyed by water or oxygen, this will result in problems in storing the product. Another problem which can arise in storage is that the additive migrates as a consequence of concentration gradients, as a result of which the concentration of additive is decreased in the intended contact and reaction area.
Some of these problems can be overcome by using a carrier for the additive. In this context, carrier means a material which has the function of storing the additive until the product is used. During use, the additive is to be released and to react and/or be transferred to the skin. Some common functions of the carrier are to protect the additive during storage, to help during and to control release of additive and/or the transfer of additive to the skin of the user.
Some examples of carrier are indicated in WO 92/13577, in which publication it is proposed that a carrier with adhesive properties, such as wax or vegetable oils, is used as the carrier for an additive, in this case lactobacilli. U.S. Pat. No. 5,968,025 also discloses how wax is used as a carrier for an additive.
It is common to use various kinds of film to produce a carrier. In U.S. Pat. No. 4,790,836, use is made of a water-soluble film which is applied to the liquid-permeable surface layer. The additive is arranged between these layers and is released when the water-soluble layer becomes moist and thus dissolves.
The carrier is often located on the surface layer but can alternatively be located on the absorbent body or in an intermediate layer in the absorbent article. As far as application or addition of additive to the carrier is concerned, there are also a great many different methods. One method is quite simply to apply the additives to the carrier ply to which they bond mechanically or chemically. Another way is to manufacture a composite consisting of carrier/additive and add this onto or into the absorbent article.
Although the known carriers bring about an improvement in terms of undesirable migration in the absorbent article, these carriers still have shortcomings. For example, the problem with moisture-sensitive additives such as lactobacilli is not solved in a satisfactory manner by the previously known art.
A carrier which can release its additive under the correct conditions results in more effective utilization of the additive. Controlling the release and transfer of additives has become increasingly important. It is a complex function which requires specific properties of the carrier and is dependent on the chemical and physical properties of the additive and also on where and for what purpose the additive is to be used. There are a number of different ways of controlling and stimulating the release. If the additives are located on the surface layer, they are often released as a consequence of mechanical mechanisms, for example pressure forces and shear forces, which press the additive out of the surface or quite simply scrape it off. This process often takes place in combination with the carrier used changing viscosity with temperature. The carrier becomes more fluid, and in this way the transfer of the additive to the skin is facilitated. In such cases, the carrier is often transferred to the skin with the additive. In the patent U.S. Pat. No. 4,790,836 mentioned above, the release takes place as a consequence of a liquid-soluble layer being dissolved. In patent application U.S. 2002/022427, a surface layer breaks as a consequence of stresses applied and a duct for release of additive is opened. WO 01/47567 indicates that an additive is applied directly to fibers which are formed into a textile material, for example a nonwoven layer. The additive is released from the textile or the nonwoven layer and begins to diffuse as a consequence of movement and increased temperature.
Depending on which additive is to be released, there are different requirements for the carrier. Recently, there has been great interest in using lactobacilli or other lactic acid-producing microorganisms in sanitary towels and tampons. The lactobacilli occur naturally in the genitals of a woman and form part of the defense against infections in the genitals. By adding lactobacilli, the body's own good bacterial flora is strengthened. One of the major problems with lactobacilli in hygiene products is avoiding moisture during storage. A product which contains lactobacilli is destroyed if the water activity (aw) in the product is about 0.2-0.8. Within this range, the supply of water is sufficient for metabolism to take place in the lactobacilli but too small for it to be possible for them to reproduce. The lactobacilli will die as a consequence of excessively active metabolism if they are not protected from moisture. The range indicated above corresponds to the conditions which can be expected to prevail in a product during storage in a normal indoor environment.